In a database management system (DBMS), data is stored in one or more data containers, each container contains records, and the data within each record is organized into one or more fields. In relational database management systems, the data containers are referred to as tables, the records are referred to as rows, and the fields are referred to as columns. In object oriented databases, the data containers are referred to as object classes, the records are referred to as objects, and the fields are referred to as attributes. Other database architectures may use other terminology.
Database management systems retrieve information in response to receiving queries that specify the information to retrieve. In order for a database management system to understand the query, the query should conform to a database language recognized by the database management system, such as the Structured Query Language (SQL).
In an OLAP (on-line analytical processing) environment or a data warehousing environment, data is often organized into a star schema. A star schema is distinguished by the presence of one or more relatively large tables and several relatively smaller tables. Rather than duplicating the information contained in the smaller tables, the large tables contain references (foreign key values) to rows stored in the smaller tables. The larger tables within a star schema are referred to as “fact tables”, while the smaller tables are referred to as “dimension tables”. Typically, each dimension has “levels” which correspond to columns of the dimension table, which are organized in a hierarchical manner. For example, a TIME dimension might consist of the levels year, quarter, month, and day, corresponding to columns of the TIME table. The hierarchical organization is such that years consist of quarters, quarters consist of months, and months consist of days.